Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $63.89   6.381%   $67.9668   $67.97   $67.95   $68.00  
  Purchase #2 $245.53   4.283%   $256.046   $256.05   $256.05   $256.00  
  Purchase #3 $234.34   9.619%   $256.8812   $256.88   $256.90   $256.90  
  Purchase #4 $202.78   4.478%   $211.8605   $211.86   $211.85   $211.90  
  Purchase #5 $105.37   11.326%   $117.3042   $117.30   $117.30   $117.30  
  Purchase #6 $145.76   10.780%   $161.4729   $161.47   $161.45   $161.50  
  Purchase #7 $229.93   12.661%   $259.0414   $259.04   $259.05   $259.00  
  7 purchase totals = $1,227.60       $1,330.5730   $1,330.57   $1,330.55   $1,330.60